Oils are generally complex mixtures of chemical compounds characterized by a base stock and a combination of additives, collectively described as an additive package, selected to improve specific performance attributes. Both the base stock and the additive package are generally specific to a particular application and intended use and convey desired oil attributes at a level commensurate with the oil's intended application.
In a typical vehicle engine lubricating oil is pumped from a sump over and through the moving parts of the internal combustion engine. The oil is heated incidental to the combustion process and cooled to maintain a suitable operating temperature, often in the range of about 90° C. to about 110° C. An oil of specified quality grade is charged to the engine and its properties deteriorate with usage. The specified oil and any suitable equivalents have known or determined electrical resistivity properties obtained over their operating life in like engines (or other lubricated mechanisms).
Associated with the engine is a computer-based engine control system. In accordance with this invention, data for the practice of this invention is maintained and processed in such a computer-based system. The electrical resistivity properties of the suitable oils at a common operating temperature are stored in the computer system. The actual resistivity history of the current oil at a like temperature is maintained as it is used and its volume in the sump is periodically determined. This stored information is used when it is time to add new makeup or replenishing oil to the existing oil or time to drain the existing oil from the sump and replace it with unused oil. This stored information and the method of this invention are used to determine whether the new oil is suitable for use in the engine or other lubricated mechanism.
The respective volumes of retained used oil and of new oil are determined. The last value of the resistivity of the used oil and the resistivity of the new mixture are obtained. As described in detail below these volumes and resistivity values are used to compare resistivity data for the added oil with like data, stored in the computer data base, for suitable lubrication oil. If the data for the added oil does not match stored data for good oils, the operator of the vehicle of other mechanism is alerted by the on-board system.
Much of the further discussion will detail the application of this technique to identify engine oil additions made to an engine in a motor vehicle. However, it will be readily appreciated that the same general procedure may be employed to characterize engine oil additions in other engine applications such as generators, engines used in marine or aerospace applications, and even oils used for primarily non-lubricious applications such as hydraulic systems.
Lubricating oil used in internal combustion engines is a complex mixture of components historically based on a petroleum hydrocarbon base stock derived from crude oil, with additives to improve certain properties. Increasingly, however, synthetic base stocks such as polyalphaolefin (PAO) or synthetic esters and related synthetics such as alkylated napthalenes and alkylated benzenes are used.
In an internal combustion engine, these engine oils are subject to severe operating conditions and will deteriorate with use. It has been recognized that different engines and operating conditions will result in greater and lesser rates of deterioration of a specific oil. Thus a number of national and international agencies have formulated standards for engine oils which reflect their resistance to deterioration in use and thus their suitability for specific applications. These agencies include the American Petroleum Institute (API), the International Lubricant Standardization and Approval Committee (ILSAC), ACEA (Association des Constructeurs Européens d'Automobiles) and the Japanese Automotive Standards Organization (JASO) as well as individual vehicle manufacturers.
In turn, vehicle manufacturers select the specifications that will meet their requirements for lubricant performance and service life. These requirements are met by the first lubricant fill of the engine by the original vehicle manufacturer, who has capability of specifying and monitoring the quality of the fluids charged during vehicle build. However subsequent oil charges are not necessarily as well controlled and, since differences between engine oils are not always apparent to either a vehicle operator or to vehicle mechanics and technicians, it is possible for an improper or lower grade lubricant to be used.
While the consequences of application of a higher than manufacturer-specified oil grade are expected to be benign, substitution of a lower-than-manufacturer-specified grade could potentially result in engine damage. It is therefore desirable to develop a capability to identify the nature of any oil additions made to an engine so that if a lower-than-manufacturer-specified grade has been used, appropriate corrective action may be taken.
It is also desirable that the nature of the added oil be determined after it has been charged. This both offers the opportunity to take advantage of on-board instrumentation which may be useful for other purposes, and places no restriction on where a vehicle owner may obtain unused replacement or make-up oil. However, it complicates the assessment of the added oil quality, since only the characteristics of the mixed and commingled used and unused oils will be measured. Thus the effect of the unused oil will be diluted by the residual used oil so that only composite measures will be determined and appropriate data processing will be required to extract the measures attributable to the unused oil from the composite measure.
The approach is based on on-board electrical measures of oil, specifically its resistivity, which exhibits both a characteristic initial value and characteristic evolutionary trends for specific oil formulations. Oils of known characteristics will be tested to establish both the initial and the evolutionary behavior of their resistivity. Since these are specific to a given oil, they will constitute a characteristic signature for a particular oil formulation. These data may then be collected and stored, for example as a look-up table in a computer storage device, where they may be accessed and compared with comparable data gathered from unknown oils. With increasing testing of known oils, a comprehensive data collection representative of the behavior of all tested oils will be developed.
Thus the resistivity changes of an unknown oil during use may be monitored for a period of time appropriate to record sufficient recognizable and characteristic features of the evolutionary profile which may be compared to the stored behaviors of known oils. When the behaviors of the unknown oil and a specific known oil are judged to be substantially identical, the unknown oil formulation will be judged identical to the formulation of the known oil.